1. Field of the Invention
The present invention relates to a novel alkenyl-substituted bisnadimide, which is a thermosetting resin exhibiting excellent processability, heat resistance, mechanical strength, electrical characteristics, a process for manufacturing said alkenyl-substituted bisnadimide, and a process for curing the same. Further, the present invention also relates to an adhesive and a coating material comprising said novel alkenyl-substituted bisnadimide as a curing component. The novel alkenyl-substituted bisnadimide is useful as a laminating material, a cast molding material, a molding material, a coating material, a paint, an adhesive, a filler, and a matrix resin for composite resins in which glass or carbon fibers are used as a reinforcing material. In particular, this alkenyl-substituted bisnadimide exhibits superior heat resistance for a long period of time when used as an adhesive, and exhibits excellent resistance to boiling water when used as a coating material.
2. Description of the Prior Art
There is an increasing demand for high performance and high functional materials along with the advance of science and technology. A great number of materials are being developed in order to satisfy this demand. Among these materials, applications of thermosetting resins have expanded to cover wide areas, including the areas of structural materials for air crafts and the like, and the areas of electronic or electrical materials, such as packaging materials for semiconductors, laminating materials, coating materials, and adhesives. A characteristic particularly demanded of such thermosetting resins is excellent heat resistance. Further, various high performance polymers, which are generally called super engineering plastics, such as polyether ketones, polyphenylene sulfides, and polyimides, have been introduced to the market. Among these, polyimides are materials of which the demand is expected to expand in future.
Bisnadimide compounds possessing norbornene rings at the both ends and aromatic groups in the molecule have heretofore attracted a great deal of attention as a raw material for addition-type polyimide resins with extremely high heat resistance. Some of them have already been used as a matrix of forerunner composite materials. The bisnadimide compounds, however, have drawbacks in their high melting point, the insufficient solubility in solvents, and the poor reactivity. These render these compounds difficult to handle and require severe reaction conditions to polymerize (e.g., 300.degree. C. or higher molding temperature). The reactions under severe conditions not only promote polymerization reaction but also partly accompany a reverse Diels-Alder reaction which produces volatile cyclopentadiene. The cyclopentadiene vapor causes a great number of boids to be produced in the molded products, impairing properties thereof. Therefore, the application of bisnadimide is considerably limited. Molding of a bisnadimide resin is therefore limited to a process using a high temperature under high pressure, such as the autoclave molding process, or it can only be used as a vanish produced by the oligomerization of raw materials of bisnadimide, i.e., a nadic anhydride or an ester thereof and a diamine, dissolved in a solvent.
Various processes for introducing suitable substituent groups to the norbornene ring of bisnadimide are investigated in order to eliminate these drawbacks in bisnadimide.
One of the processes is introducing alkenyl groups such as allyl group or methallyl group, and a number of proposals dealing with this process have been reported, e.g., U.S. Pat. Nos. 4,515,962, 4,579,916, 4,604,437, 4,666,997, 4,678,849, 4,709,047, 4,728,742, 4,777,236, 4,778,898, 4,885,346, 4,966,923, 5,120,857, Japanese Patent Laid-open No. Sho 63 (1988)-170358 and No. Sho 63 (1988)-310884, etc.
These proposals claim that the introduction of alkenyl groups, such as allyl group or methallyl group, lowers the melting point of the nadimide, increases its solubility in solvents, lowers curing temperature to a certain degree, and prevents production of volatile matters when the resin is cured, while without substantially injuring properties of the resulting cured resin. These alkenyl-substituted nadimides are thus considered to exhibit excellent processability, and their thermoset products are deemed to have superior heat resistance, mechanical strength, electrical characteristics, and chemical stability. These are thus useful in some degree as a laminating material, molding material, composite material, coating material, paint, or adhesive. However, these alkenyl-substituted nadimides are insufficient and still to be improved in their mechanical properties, especially in toughness, and in their adhesion characteristics to substrates.
In the field of heat resistant adhesives, thermosetting polyimides, such as bismaleimide, polyamino-bismaleimide (KERIMIDE, tradename, Ciba-Geigy AG) , and triazine-modified bismaleimide (BT Resin, tradename, Mitsubishi Gas Chemical Company, Inc.), have been known conventionally. The alkenyl-substituted nadimides are also known to be usable as a heat resistant adhesive. These conventional imides, however, are still insufficient in their heat resistance when used as an adhesive for a long period of time at a high temperature.
Further, in the field of coating materials a number of thermosetting polyimides, including said alkenyl-substituted nadimides, are also known to be usable as coating materials. These conventional thermosetting polyimide type coating materials are insufficient in their resistance to boiling water, when applied to surfaces exposed to boiling water or high temperature steam, such as hot water boilers, boiling water tanks, and hot water pipes.